When it comes to smart personal finance and building wealth, there's really only one basic rule you have to remember: spend less than you earn and invest the difference. It's old advice to a lot of people, but bears repeating.

The most fundamental rule of personal finance is to spend less than you earn. If you invest the difference, you can make the surplus grow. That's it; everything else is in the details.

J.D. Roth says at the Get Rich Slowly blog that writers tend to focus on finding "new and unique" money tips, avoiding the basics for fear of boring readers with the same old solution. But old advice to some people is new to others (e.g., to recent graduates now managing their finances).